• DOI:10.1073/pnas.1513439112
• Corpus ID: 4506561

An invertebrate smooth muscle with striated muscle myosin filaments

@article{Sulbarn2015AnIS,
  title={An invertebrate smooth muscle with striated muscle myosin filaments},
  author={Guidenn Sulbar{\'a}n and Lorenzo Alamo and Antonio Pinto and Gustavo M{\'a}rquez and Franklin J. M{\'e}ndez and Ra{\'u}l Padr{\'o}n and Roger Craig},
  journal={Proceedings of the National Academy of Sciences},
  year={2015},
  volume={112},
  pages={E5660 - E5668}
}

• G. Sulbarán, L. Alamo, +4 authors R. Craig
• Published 6 October 2015
• Biology
• Proceedings of the National Academy of Sciences

Significance All animals have the ability to move. In most animals, striated muscles move the body and smooth muscles the internal organs. In both muscles, contraction results from interaction between myosin and actin filaments. Based on vertebrate studies, smooth and striated muscles are thought to have different protein components and filament structures. We have studied muscle ultrastructure in the parasite Schistosoma mansoni, where we find that this view is not supported. This invertebrate possesses only smooth muscles, yet its myosin sequence and filament structure are identical to those of striated muscle, while its actin filaments are smooth muscle-like. Such “hybrid” muscles may be common in other invertebrates. This finding challenges the paradigm that smooth and striated muscles always have different components. Muscle tissues are classically divided into two major types, depending on the presence or absence of striations. In striated muscles, the actin filaments are anchored at Z-lines and the myosin and actin filaments are in register, whereas in smooth muscles, the actin filaments are attached to dense bodies and the myosin and actin filaments are out of register. The structure of the filaments in smooth muscles is also different from that in striated muscles. Here we have studied the structure of myosin filaments from the smooth muscles of the human parasite Schistosoma mansoni. We find, surprisingly, that they are indistinguishable from those in an arthropod striated muscle. This structural similarity is supported by sequence comparison between the schistosome myosin II heavy chain and known striated muscle myosins. In contrast, the actin filaments of schistosomes are similar to those of smooth muscles, lacking troponin-dependent regulation. We conclude that schistosome muscles are hybrids, containing striated muscle-like myosin filaments and smooth muscle-like actin filaments in a smooth muscle architecture. This surprising finding has broad significance for understanding how muscles are built and how they evolved, and challenges the paradigm that smooth and striated muscles always have distinctly different components.